The present invention relates to vehicle differentials, and specifically to an apparatus and method for setting pinion bearing preload and fastener clamp load.
A vehicle differential performs several functions. The differential turns the flow of power 90 degrees from the engine drive shaft to the vehicle wheels, reduces drive shaft revolutions to a useful wheel speed, and divides power between the rear wheels so one wheel can rotate at a different speed than the other such as when the outer wheel turns faster in order to go the long way around the outside of a curve while the inner wheel slows down to follow the shorter inside path. The differential includes a housing, a drive pinion extending into the housing with a pinion gear that engages a ring gear. The ring gear carries small pinions and side gear which are coupled to the axle shafts.
The pinion gear is supported by pinion bearings which are placed in a preloaded condition to maintain alignment of the pinion drive shaft during operation. Pinion bearings are supplied as two basic components, a cone assembly including a cone, also known as an inner race, a cage and rollers, and a cup also known as an outer race. Preload is a bearing setting in which there is no axial clearance in the bearing. The preloaded condition is achieved by tightening the bearing setting to have a slight amount of resistance to rotation. The greater the preload the more resistance to rotation. The pinion bearing preload is often confirmed by measuring the pinion bearing preload rolling torque according to methods well known in the art. Too much preload, and the bearings may wear prematurely, no preload and the bearings may allow play in the system. Thus, the desired level of pinion bearing preload in a differential can minimize shaft bending helping to maintain alignment between the pinion gear and ring gear, can reduce seal wear, and can reduce noise.
Various methods have been employed to set pinion bearing preload. One exemplary design is described in U.S. Pat. No. 3,308,682 entitled Differential Gear Assembly. This patent provides for a shim between an inner bearing and the housing, and an additional collapsible spacer inboard of an outer bearing and between the outer bearing and portion of the pinion shaft, both the shim and collapsible spacer being provided to set a desired pinion bearing preload. In this design, a nut is threaded onto the pinion drive shaft and into contact with a cone of the outer bearing. The torque applied to the nut is proportional the amount of preload developed on the bearings and axial force of the collapsible spacer, regardless of what torque is applied. Thus if the preload is too low, the nut is tightened further against the bearing, and if the preload is too high, the unit must be disassembled and reassembled with a new spacer. In either case, the nut is retained in place by the additional step of staking or crimping a circumferential flange of the nut to engage the splines of the drive pinion shaft.
A major difficulty encountered in such a design is retention of the nut preload force under heavy reversing loads. More specifically, heavy loads with shock often encountered in off highway applications tend to cause the nut to back off due to lack of adequate locking force. This allows the bearings to loosen and may result in earlier failure of components in the differential.
The inventor of the present invention has recognized the need for and has invented an improved apparatus and method for setting pinion bearing preload and improved nut locking force. The invention provides for consistent pinion bearing preload in initial manufacture of the differential, proper maintenance of pinion bearing preload over time, and ease of setting proper pinion bearing preload upon repair and re-assembly of the differential. The invention provides superior nut locking force which maintains proper bearing setting for the life of the design. The present invention addresses these needs and others.
The present invention provides a vehicle differential with an improved structure and method for setting pinion bearing preload and fastener clamp load. The apparatus and method utilize a preload spacer readily accessible outboard of an outer bearing set to limit the preload applied to an inner and outer bearing, and to allow for increased clamp load between a nut and a threaded shank extending from a pinion drive shaft.
A differential according to the present invention includes a housing, an inner bearing cup and outer bearing cup in direct contact with the housing. An inner cone assembly and outer cone assembly are supported within the inner bearing cup and outer bearing cup. A pinion drive shaft includes a shaft supported within the inner and outer cone assemblies, a pinion gear at a first end of the shaft in contact with the inner cone, and a shank extending from a shoulder at a second end of the shaft. The second end of the shaft extends outboard of the outer cone. An input yoke is coupled to the second end of the shaft between the outer cone and the shank and is in engagement with the outer cone. A nut is disposed about the shank and is in engagement with the input yoke and a preload spacer. The preload spacer is disposed between the nut and the shoulder, and serves to limit the movement of the nut against the input yoke, this provides for consistent displacement of the input yoke and pinion drive shaft relative to one another resulting in consistent preload on the pinion bearings and increased clamp load between the nut and shank. The present invention additionally provides a method for controlling pinion bearing preload in a differential.